During the production of glass bottles, a series of defects can be produced in the sealing surface of the bottle mouth. In order to ensure that the sealing surface can cooperate in a problem-free manner with the closure element provided and in particular leakages are obviated, it is important to detect wrinkles extending e.g. radially over the mouth surface and to separate out the corresponding containers. Other possible flaws in the sealing surface include nicks, orange peel or even other defects. Cracks in the sealing region of a drinks bottle can be the starting point of localized breakage of the mouth lip and thus represent a risk for a consumer drinking from the bottle.
It is known to detect defects in the sealing surface by virtue of the fact that light is transmitted on to the sealing surface and a camera serves to detect light which is diffusely scattered by flaws in the sealing surface. A testing device which is known in practice is illustrated in FIG. 1. The known testing device is designated by the reference numeral 1. Located below the testing device 1 is a glass bottle 2 which is shown only partially and in which a sealing surface 3 of a mouth 4 is examined by means of the testing device 1.
The testing device 1 comprises a light source 5 which emits light beams 9 perpendicularly or almost perpendicularly on to a diffuser disc 10. The diffuser disc 10 comprises an orifice 11 in the center.
A diffuse reflector 13 is disposed below the diffuser disc 10. The reflector 13 is positioned in the shape of a collar around the mouth 4 and comprises a reflective inner surface 14. The reflector 13 comprises a lower orifice 15, below which the mouth 4 is positioned. The reflector 13 can be produced e.g. from iron and can comprise on the inner surface 14 a white color layer to reflect the light. A camera 18 operating as a sensor is disposed above the orifice 11 of the diffuser disc 10 symmetrically with respect to a longitudinal axis 16 of the mouth 4. A housing of the testing device 1 is not shown in FIG. 1. The light which is emitted by the light source 5 on to the diffuser disc 10 consists not only of parallel light beams 9 but also of light beams, not illustrated, which do not impinge perpendicularly upon the diffuser disc 10. The light source 5 can comprise e.g. a series of light-emitting diodes, not illustrated, which have a reflected beam opening angle of 30 to 40°. By virtue of the diffuser disc 10, the impinging light becomes diffuse, i.e. is scattered in all directions. By way of example, two scattered light beams 21 and 22 are illustrated. Further scattered light beams are illustrated in rudimentary fashion at 23. The light beam 21 impinges upon the reflector 13 in parallel with the mouth longitudinal axis 16. In turn, the light according to light beam 21 is scattered by the reflector in all possible directions, as illustrated by the light beam 24 and at 25 by rudimentary light beams.
The light beam 24 passes through the orifice 15 of the reflector 13 on to the sealing surface 3. Since the sealing surface 3 is smooth, the light beam 24 is reflected at an angle corresponding to the inclination of the glass surface. The resulting reflected light beam is designated by the reference numeral 26. The reflected light beam 26 also results from a scattering of the light beam 22 which, without previously impinging upon the reflector 13, passes on to the sealing surface 3 where it is also reflected. The two light beams 24 and 22 impinge close to one another but not exactly at the same site upon the sealing surface 3. Since the sealing surface 3 has a strong curvature in the region, both beams are reflected in beams which lie very closely next to one another, and only a resulting light beam, namely the light beam 26, is illustrated in a simplified manner. In this manner, light passes in an annular manner into the camera 18, whereby a so-called reflection ring 28 is produced, as shown in FIG. 2 which schematically illustrates a section of an image 31 recorded by the camera 18. For the sake of completeness, it should be mentioned that some of the light which impinges upon the sealing surface 3 is broken and enters into the glass of the mouth 4.
A further reflection ring 29 is produced by corresponding reflection of light beams at an inner edge 30 of the mouth 4. Since the inner edge 30 has a very much stronger curvature, not illustrated, than the outer edge 27, the inner reflection ring 29 is narrower than the outer reflection ring 28. For the sake of clarity, FIG. 1 does not illustrate light beams which produce the reflection ring 29.
Although light which impinges between the outer edge 27 and the inner edge 30 upon the sealing surface 3 is reflected in a particular direction, it does not impinge upon the camera 18. Therefore, in the camera image 31 this region normally appears dark. At defective points on the sealing surface 3, such as wrinkles, nicks, orange peel or similar deflects, impinging light is diffusely scattered. By reason of this diffuse scattering, light is also scattered into the camera 18 by these defects. By way of example, FIG. 2 illustrates the case where a wrinkle extends approximately in the radial direction over the sealing surface 3. The wrinkle serves to produce in the camera image 31a corresponding bright line 33 which extends between the two reflection rings 28, 29.
A problem which arises in practical usage resides in the fact that the intensity of the reflection rings 28, 29 is generally considerably greater than the intensity of the light 33 which passes into the camera 18 by reason of a defect in the sealing surface 3. The defect image 33 becomes superimposed by virtue of the reflection rings 28, 29, thus making it more difficult to detect defects in the sealing surface 3.
DE 35 18 653 C2 discloses a generic method and a generic device respectively. In order to examine the bottle mouths for defects, interfering reflections of flawless regions of the mouth are obviated by virtue of the fact that specific mouth regions are shielded from a light source. For example, this relates to an upper mouth region (see FIG. 4A). A disadvantage of this shield is that defects cannot be detected in the shielded mouth regions. Furthermore, it is also disclosed in the named document to utilize a shield in order to ensure that light beams which have a tangential orientation impinge upon the mouth region which is to be examined (see FIG. 4B). Light beams which impinge tangentially upon the mouth region which is to be examined are not reflected upwardly and thus not into a camera which is disposed above the mouth, unless there is a defect in the mouth region. In order to achieve the desired degree of shielding, relatively complex light-guiding devices are required, e.g. an annular element having tangentially aligned holes or light-guiding plates. Moreover, a disadvantage of the known testing device is that it is not achieved to uniformly illuminate the sealing surface which is to be examined and light intensity on the whole is lost by virtue of the shielding arrangement. It is also not possible to achieve a tangential deflection simultaneously on both sides using the described light-guiding devices.
DE 36 86 847 T2 describes a testing device for detecting defects on a bottle neck which is provided with a screw thread. In the case of this known testing device, a tangential illumination of the region to be examined is also provided. The tangential illumination is achieved in turn by means of bores in an annular illumination device (see in particular FIGS. 3 and 4).
DE 39 40 693 C1 discloses a device for examining mouth regions, in which the principle of dark field illumination is applied. The light is transmitted in a radial direction on to a bottle mouth. Light is reflected into the camera only by the lips of the bottle mouth. There is no tangential illumination provided to obviate undesired reflections.
EP 0 657 732 A1 describes a device for optically examining a transparent mouth region, in which the region to be examined is observed in transmitted light by means of a substantially homogeneous light-radiating surface below said region to be examined. This testing method is not based upon the evaluation of reflections.
For the purpose of examining the mouth region, U.S. Pat. No. 4,731,649 describes an illumination device which is disposed substantially radially with respect to the mouth and which transmits light diffusely on to the region below the top edge of the mouth. A selective tangential irradiation is not provided.
In U.S. Pat. No. 2,868,061 there is provided a testing device for examining mouths of glass containers, in which a photomultiplier is used as a sensor. There is no provision to transmit light selectively in a tangential manner on to the mouth.
WO 90/04773 describes an optical system for recording an image for examining container mouths, wherein, however, no illumination device is used.
DE 31 47 086 A1 describes a device, in which light impinges tangentially upon a bottle mouth by means of a light conductor.